Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

167
FXUS63 KLOT 261113
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
613 AM CDT Fri Jun 26 2026

.KEY MESSAGES...

- Showers will affect areas generally south of I-80 today and
  tonight, and especially south of U.S. 24 where rainfall could
  be heavy at times.

- A few thunderstorms are possible Saturday night into Sunday
  morning.

- Dangerous heat will build across the area next week, with
  afternoon heat index values over 100 degrees each day
  beginning Monday.

&&

.DISCUSSION...
Issued at 241 AM CDT Fri Jun 26 2026

Early morning analysis shows a convectively-enhanced wave over
southeast Kansas beginning a trek along a WSW-ENE oriented
stationary front. This wave should continue follow along the
front today, crossing the southern third of Illinois by this
evening. This activity is somewhat farther south than earlier
guidance indicated, supporting at least a downward trend in PoPs
for areas north of the Kankakee River Valley. In fact, areas
north of I-80 may remain dry. However, a substantial moisture
gradient on the northern periphery of the incoming wave suggests
the potential for a notably sharp QPF gradient over or just
south of the southern CWA. South of the gradient, PWAT values
around 2", a relatively warm profile (10kft deep moist layer
warmer than -10C), and seasonably strong dynamics will yield
high rainfall rates, and may result in a narrow corridor of
heavy rain somewhere across central Illinois this afternoon and
evening. Would not be surprised to see 1-2" amounts south of the
U.S. 24 corridor by late this evening, but chances for higher
impact rainfall look to remain around and south of I-74.

Lingering showers across the far southern CWA early Saturday
should end by late morning. Saturday will then feature gradually
clearing skies and highs around 80 (cooler lakeside).

Primary focus then turns to developing dangerous heat across
the region next week. A building ridge over the central Great
Plains early this weekend will drift ENE through Sunday night,
with the core of the ridge settling over the lower Ohio River
Valley for much of next week.

Developing convection toward the Mississippi River Saturday
evening in response to weak isentropic ascent ahead of an
approaching EML will encounter a gradually less favorable
environment with northeast extent through the night. Given
marginally favorable low-level moisture profiles and modest mid-
level lapse rates, expectations are that elevated convection
should survive at least into the southwest CWA overnight before
fully decaying toward northeast Illinois by daybreak Sunday.
Following any precip potential early Sunday, heat and humidity
will begin to build with heat index values rising into the 90s
during the afternoon.

Concerns for dangerous heat will quickly grow beginning Monday
as a constant feed of Gulf moisture arrives over the area.
Afternoon heat index values will likely rise over 100 beginning
Monday and persist possibly through the entire week. Meanwhile,
nighttime temps will struggle to fall much into the 70s, and may
remain near 80 over the core of the Chicago metro for several
nights. Early in the week, there looks to be little relief from
lake breezes or upstream convection as substantial capping and
the strength of the ridge deflect most activity well to the
northwest over Minnesota and northern Wisconsin. By Thursday,
weakening of the cap may allow more robust convective complexes
to near from the north and provide some relief for northern
portions of the area. If this does not occur, similar heat will
likely continue heading into the Independence Day weekend.

Kluber

&&

.AVIATION /12Z TAFS THROUGH 18Z SATURDAY/...
Issued at 613 AM CDT Fri Jun 26 2026

Aviation forecast concerns for the 12Z TAFs:

- Scattered SHRA near/south of the Chicago terminals mid-morning
  through this afternoon. Farthest south KGYY has the highest
  chance (30-40%) of seeing rain at the airfield.

- Low-confidence (10-20%) for patchy MVFR ceilings off the lake
  later tonight into early Saturday for Chicago terminals.

Surface low pressure wave was analyzed near the OK/KS border
early this morning, with a nearly stationary frontal boundary
extending northeast and east through central IL/IN. The surface
wave is expected to track east along the frontal zone today,
spreading rain south of most of the terminals across primarily
central IL/IN. Model trends have backed-off the northward extent
of RA/SHRA, and while a few sprinkles can`t be ruled out
farther north, scattered SHRA are expected mainly south of
KORD/KDPA and even KMDW (though precipitation may come close to
KMDW). KGYY looks to have the greatest potential (30-40%) of
actually seeing a period of -RA/SHRA at the airfield, and have
indicated a PROB30 there along with an MVFR ceiling later this
morning and afternoon from 15Z-21Z while maintaining a VCSH
mention for KMDW. Thunder potential continues to appear quite
low (<10%) given poor low-mid level lapse rates. VFR conditions
are expected for all sites, though there is a low (10-20%)
probability of some MVFR ceilings developing off of Lake
Michigan later tonight into early Saturday morning for the
Chicago terminals.

Surface winds are expected to be from the east to northeast
through the period, generally 10 kts or less.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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